450 – Transformers and Transformer Vaults (Including Secondary Ties)

450.9 – Horizontal Top Surfaces of Transformers Prohibited as a Storage Area

Change at a Glance:

New sentence was added to prohibit horizontal top surfaces of transformers from being used as a storage area.

450.9 Ventilation. (Transformers)

The ventilation shall dispose of the transformer full-load heat losses without creating a temperature rise that is in excess of the transformer rating.
Informational Note No. 1: See ANSI/IEEE C57.12.00-1993 2015, General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers, and ANSI/IEEE C57.12.01-1993 2015, General Requirements for Dry-Type Distribution and Power Transformers.
Informational Note No. 2: Additional losses may occur in some transformers where nonsinusoidal currents are present, resulting in increased heat in the transformer above its rating. See ANSI/IEEE C57.110-1993 2008, Recommended Practice for Establishing Liquid-Filled and Dry-Type Power and Distribution Transformer Capability When Supplying Nonsinusoidal Load Currents, where transformers are utilized with nonlinear loads.
Transformers with ventilating openings shall be installed so that the ventilating openings are not blocked by walls or other obstructions. The required clearances shall be clearly marked on the transformer. Transformer top surfaces that are horizontal and readily accessible shall be marked to prohibit storage.